U.S. patent number 6,111,526 [Application Number 09/147,613] was granted by the patent office on 2000-08-29 for vehicle course steering aid device.
This patent grant is currently assigned to Sextant Avionique. Invention is credited to Bruno Aymeric, Roger Parus.
United States Patent |
6,111,526 |
Aymeric , et al. |
August 29, 2000 |
Vehicle course steering aid device
Abstract
A device for assisting the piloting of a vehicle by instruments.
Various indications are displayed on an aircraft head-up view
finder including a horizontal line graduated in terms of heading, a
perpendicular line graduated in terms of atitude, an aircraft
symbol representing the direction of the longitudinal axis of the
aircraft above the horizontal line and a velocity vector symbol
representing the tracking slope followed by the aircraft with
respect to the ground. These are determined with respect to the
tracking and atitude scales. The guidance window whose position is
references with respect to the same axis is also displayed. The
pilot must control the aircraft as to bring the velocity vector
into the guidance window and keep it there. The window is placed on
the screen at a position which is computed by the computer and
which corresponds to the direction of a point of the desired path
of the aircraft, this point being at a predetermined distance ahead
of the aircraft.
Inventors: |
Aymeric; Bruno (Le Taillan,
FR), Parus; Roger (Merignac, FR) |
Assignee: |
Sextant Avionique (Velizy
Villacoublay, FR)
|
Family
ID: |
9494784 |
Appl.
No.: |
09/147,613 |
Filed: |
February 2, 1999 |
PCT
Filed: |
July 29, 1997 |
PCT No.: |
PCT/FR97/01414 |
371
Date: |
February 02, 1999 |
102(e)
Date: |
February 02, 1999 |
PCT
Pub. No.: |
WO98/05928 |
PCT
Pub. Date: |
February 12, 1998 |
Foreign Application Priority Data
|
|
|
|
|
Aug 2, 1996 [FR] |
|
|
96 09804 |
|
Current U.S.
Class: |
340/972; 244/181;
244/183; 340/973; 340/974; 701/14; 701/16; 73/178R; 73/178T |
Current CPC
Class: |
G05D
1/0676 (20130101); G01C 23/005 (20130101) |
Current International
Class: |
G01C
23/00 (20060101); G05D 1/06 (20060101); G05D
1/00 (20060101); G01C 023/00 () |
Field of
Search: |
;340/972,973,974,980,971
;244/181,182,183 ;701/16,14 ;73/178T,178R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lee; Benjamin C.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. Device for assisting the piloting, or the simulation of the
piloting, of a vehicle, this device comprising means for
determining the current position of the vehicle, a generator of
symbols for aiding piloting, means for displaying these symbols,
which include a velocity vector symbol whose position on the
display means represents the direction of movement of the vehicle
with respect to the ground and a guidance symbol whose position on
the display means represents a datum direction in which the vehicle
ought to move so as to join up with a predetermined path and means
for computing this datum direction from the current position and
from information about the said predetermined path, characterized
in that the datum direction computed by the said computing means is
the direction of the straight line connecting the current position
of the vehicle to a datum point situated on a guidance path
corresponding to the said predetermined path and a predetermined
datum distance d away from the said position of the vehicle.
2. Device according to claim 1, characterized in that the guidance
path comprises at least one theoretical path segment which the
vehicle should follow or join up with.
3. Device according to claim 2, characterized in that the
predetermined path of the vehicle is a diagrammatic representation
of a real path which the vehicle ought to follow.
4. Device according to claim 2, characterized in that the
predetermined distance d is modifiable from one flight phase to
another.
5. Device according to claim 1, characterized in that the guidance
path comprises at least one path segment deduced by computing a
theoretical path segment which the vehicle should follow or join up
with.
6. Device according to claim 5, characterized in that the path
segment deduced by computation is a segment parallel to the
theoretical path segment.
7. Device according to claim 6, applied to the case of the landing
of an aircraft, characterized in that the theoretical path segment
is the axis of a runway and the corresponding guidance path segment
is a segment parallel to this axis and situated under the runway at
a depth allowing impact of the aircraft on the runway at a non-zero
predetermined angle.
8. Device according to claim 7, characterized in that the
predetermined path of the vehicle is a diagrammatic representation
of a real path which the vehicle ought to follow.
9. Device according to claim 6, characterized in that the
predetermined path of the vehicle is a diagrammatic representation
of a real path which the vehicle ought to follow.
10. Device according to claim 5, characterized in that the
predetermined path of the vehicle is a diagrammatic representation
of a real path which the vehicle ought to follow.
11. Device according to claim 5, characterized in that the
predetermined distance d is modifiable from one flight phase to
another.
12. Device according to claim 6, characterized in that the
predetermined distance d is modifiable from one flight phase to
another.
13. Device according to claim 1, characterized in that the
predetermined path of the vehicle is a diagrammatic representation
of a real path which the vehicle ought to follow.
14. Device according to claim 13, characterized in that the
predetermined path is a string of broken straight-line
segments.
15. Device according to one of claim 1, characterized in that the
predetermined distance d is modifiable from one flight phase to
another.
16. Device according to claim 15, characterized in that the
predetermined distance d is modified continuously between two
values corresponding to two different flight phases so as to avoid
abrupt jumps in the position of the guidance symbol on the display
screen during changes in the value of this distance.
17. Device according to claim 1, applied to the landing of an
aircraft, characterized in that the guidance path comprises at
least one ideal descent straight-line segment situated along the
axis of a runway, and a straight-line segment parallel to the axis
of the runway, situated under the runway in a vertical plane
containing this axis.
18. Device according to one of claim 1, characterized in that the
guidance symbol is displayed on the screen at a position whose
co-ordinates are defined in one and the same track and slope
reference frame as the velocity vector symbol so that the vehicle
is situated on a desired path segment when the velocity vector
symbol is centred on the centre of the guidance symbol.
19. Device according to claim 1, characterized in that the guidance
symbol consists of a rectangular window.
20. Device according to claim 19, characterized in that the
rectangular window has dimensions corresponding to a maximum
tolerated deviation in position with respect to an ideal
theoretical path segment which the vehicle must follow, so that if
the centre of the velocity vector symbol remains situated in the
window, then the vehicle is definitely inside the limit of
permitted deviation.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for assisting the
piloting or the simulation of the piloting of a vehicle. It applies
mainly to aircraft, but it can be applied also to all sorts of
other air, land or sea vehicles, especially when they are
manoeuvred in a three-dimensional space. The invention will be
described with regard to the piloting of an aircraft, and in
particular the piloting in the landing phases.
2. Discussion of the Background
Under manual piloting, the pilot acts by sight to modify the
direction of movement of his vehicle for the aid of the trim and
engine controls.
Assistance with the manual piloting of an aircraft can be carried
out by displaying, in front of the pilot's eyes, symbols
representing the terrestrial environment and the movement of this
aircraft, these symbols being superimposed, when the visibility is
sufficient, with the real horizon and real environment seen by the
pilot through the windscreen of his vehicle. The position and shape
of the symbols are computed and displayed for example by the
computer controlling a head-up collimator from data supplied by
sensors carried on board the aircraft.
On the display screen of a known device for assisting aircraft
piloting, the artificial horizon computed is symbolized by a line
which tilts as a function of the lateral tilt (angle of roll) of
the aircraft. It is superimposed on the visible real horizon if
visibility is sufficient. It replaces it when visibility is
insufficient. The projection at infinity of the longitudinal axis
of the aircraft is portrayed by a symbol termed the "aircraft
symbol". This symbol is above the horizon line to a greater or
lesser extent depending on whether the aircraft is nose-up to a
greater or lesser extent (greater or lesser longitudinal attitude
of the aircraft); the attitude of the aircraft can be referenced by
the position of the aircraft symbol in front of an attitude scale
perpendicular to the horizon line. The lateral position of the
aircraft symbol, representing the heading followed, is referenced
moreover with respect to a graduated scale referenced with respect
to north and scrolling along the horizon line. For the pilot, the
position of the aircraft symbol on the screen portrays the
longitudinal axis of the aircraft at any moment.
For landing, the terrestrial environment reconstructed on the
display screen can be supplemented with a representation of the
runway whose characteristics are catalogued in landing strip
configuration documents which can be accessed by the computer. This
artificial representation of a runway is superimposed on the
visible real runway when the conditions of visibility are
satisfactory. It replaces it when visibility is insufficient.
Moreover, the real direction of movement of the aircraft is
different from that of its longitudinal axis, especially on account
of sidewind and on account of the fact that the aerodynamic forces
which keep the aircraft aloft and its transverse accelerations
originate from the tilt of the wing with respect to the direction
of movement. This is why the direction of real movement of the
aircraft is represented on the screen by a particular symbol
generally called the velocity vector. This movement symbol
represents the direction of the real velocity vector of the
aircraft with respect to the ground; it is defined by two
orthogonal components which are on the one hand the drift of the
aircraft in a horizontal plane and on
the other hand the climb or descent slope of the aircraft with
respect to the horizontal plane.
The drift is the angle between the track and the heading of the
aircraft, where the direction of the track is defined by the
horizontal component of the velocity of the aircraft with respect
to the ground, whilst the heading is defined by the direction of
the horizontal projection of the axis of the aircraft.
Additionally, the climb or descent slope of the aircraft with
respect to the ground is defined by an angle whose tangent is the
ratio of the vertical component to the horizontal component of the
real speed of the aircraft with respect to the ground.
The velocity vector symbol, that is to say the direction of real
movement of the aircraft, can be represented on the display screen
in a reference frame consisting on the one hand of the moving
horizon line, graduated in angular units of heading, and on the
other hand of an axis perpendicular to the artificial horizon line,
graduated in angles of climb or descent. The velocity vector symbol
is placed on the screen at a position referenced with respect to
these two axis, as a function of drift (plotted as abscissa along
the horizon line) and slope (plotted as ordinate on the axis
perpendicular to the horizon line). Drift and slope are computed by
the on-board instruments. The pilot can ascertain the drift and the
slope at any moment by looking at the position of the symbol with
respect to these two axes.
With such a piloting device, the pilot can carry out his manoeuvres
by controlling the aircraft movement symbol directly on the display
screen in front of his eyes, in particular when visibility is
insufficient.
This piloting is further aided by the displaying on the screen, at
each instant, of a guidance symbol computed by the computer as a
function of a theoretical direction to be followed. Piloting then
consists in acting on the controls of the aircraft in a sense which
tends to take the movement symbol (or velocity vector) towards the
guidance symbol on the screen. When the guidance symbol has the
form of a window, piloting consists in trying to keep the movement
symbol within the window representing the guidance symbol. Proper
guidance therefore depends mainly on the position of the centre of
the guidance symbol on the screen, and also on the shape and
dimensions of this symbol.
An assistance device which makes it possible to display a guidance
window in the case of assistance with landing on a runway equipped
with an ILS system (Instrument Landing System) is already known
through Patent EP 0 044 777.
In the ILS systems, allowing runway approach in poor visibility, an
ideal line of descent is proposed to the vehicle and the deviations
between this line and the actual position of the vehicle are
measured.
Thus, when the aircraft is moving in such a way that the deviations
are constantly zero, the real path of the vehicle coincides with
the ideal line.
This ideal line of descent is a line belonging to the vertical
plane passing through the axis of the runway and exhibiting an
inclination .theta..sub.0 with respect to the horizontal plane of
the ground. The inclination .theta..sub.0 is around 2.5 to 3
degrees.
FIG. 1 depicts a view of the vertical plane passing through the
axis of the runway. The ideal line of descent 10 belongs to the
vertical plane passing through the axis 11 of the runway, it is
defined there by its inclination .theta..sub.0 with respect to the
horizontal plane of the ground on the one hand and by its
intersection with the ground at the ideal point of impact G for
landing on this runway, on the other hand. The point G is on the
axis of the runway, close to the start of the runway.
In this vertical plane, a measurement of the position P of the
aircraft is performed by receiving, on an antenna aboard the
aircraft, signals transmitted by a transmitter at G, this
measurement E.sub.G, or "Glide deviation", is the difference
between the inclination of the ideal line 10 and the inclination of
the line 12 joining the projection P.sub.v in this vertical plane
of the position P of the aircraft on the one hand and the ideal
point of impact G on the other hand.
The horizontal plane parallel to the ground and passing through the
position P of the aircraft is represented by the line 17 in FIG. 1,
and its contour at infinity represents the 360 degree horizon
viewed from the position P.
FIG. 2 depicts a view from above of the runway, the axis 11 of the
runway being the line joining the point G situated towards the
start of the runway and a point L placed slightly beyond the end of
the runway. The projection P.sub.h of the position P of the
aircraft in this horizontal plane of the ground on the one hand and
the point L on the other hand define a line 20 which deviates by
the angle E.sub.L from the axis of the runway. The angle E.sub.L,
or "LOC deviation", is measured by receiving, on an antenna aboard
the aircraft, signals from a radio transmitter placed at the point
L.
The pilot therefore sees the point G at the angle (.theta..sub.0
+E.sub.G) below the horizon line, and the point L at the angle
E.sub.L with respect to the heading of the runway.
And if the ILS receiver placed aboard the aircraft indicates a
vertical angular deviation E.sub.G or a horizontal angular
deviation E.sub.L which is not zero, the aircraft is not on the
ideal line of descent.
The known assistance device displays as guidance symbol, a window
whose position is defined on the screen from the measurement of the
Glide deviation E.sub.G and LOC deviation E.sub.L angles. More
precisely, the centre of the window is, on the display screen, at a
position which differs from the ideal point of impact G (in the
reference frame consisting of the moving horizon line graduated in
angular units of heading and of the axis of longitudinal tilts), by
amounts which are proportional respectively to the deviations
E.sub.L and E.sub.G with the aid of proportionality coefficients
k.sub.L and k.sub.G. The pilot must seek to bring the symbol for
the real movement of the aircraft into this window and keep it
there.
Generally, the datum settings, corresponding to the successive
positions of the centre of the guidance window, allow the vehicle
progressively to approach the ideal line and hence to align its own
path with this line. This constitutes guidance to a line.
The coefficients k.sub.G and k.sub.L regulate the damping of the
datum: for small values of these coefficients, guidance towards the
ideal line is slow and for higher values, the aircraft is directed
more rapidly towards this line.
However, it is observed that when the aircraft is at a position P
(P.sub.h, P.sub.v) close to the point G, the taking into account of
such a datum takes the vehicle beyond the ideal line and by
following the successive datum settings for such guidance, the
vehicle begins to oscillate to either side of the ideal line whilst
also reducing its distance with respect to the point G. With such
guidance, sighting up to the ideal point of impact G is
unstable.
In Patent EP 0 044 777, to obtain more stable sighting the gain
K.sub.G can vary as a function of the distance to the point G.
Moreover, the guidance law is changed in the vertical plane on
approaching the ground.
SUMMARY OF THE INVENTION
A purpose of the invention is to propose a guidance which does not
have this drawback and which has other advantages for the
pilot.
To arrive thereat, the invention proposes to display at each
instant a guidance window centred on a point in space which is
situated on a predetermined path and which is a predetermined
distance d away from the current position of the vehicle.
The invention proposes more precisely a device for assisting the
piloting, or the simulation of the piloting, of a vehicle, this
device comprising means for determining the current position of the
vehicle, a generator of symbols for aiding piloting, means for
displaying these symbols, which include a velocity vector symbol
whose position on the display means represents the direction of
movement of the vehicle with respect to the ground and a guidance
symbol whose position on the display means represents a datum
direction in which the vehicle ought to move so as to join up with
a predetermined path and means for computing this datum direction
from the current position and from information about the said
predetermined path, characterized in that the datum direction
computed by the said computing means is the direction of the
straight line connecting the current position of the vehicle to a
datum point situated on a guidance path corresponding to the said
predetermined path and a predetermined datum distance d away from
the said position of the vehicle.
The assistance system therefore computes a datum direction by
searching along the guidance path for a point situated at a
predetermined distance d ahead of the vehicle.
The predetermined path is either the exact path which the vehicle
ought ideally to follow or a simplified representation of this
path, and in particular a representation in the form of successive
straight line segments. The guidance path either coincides with the
predetermined path (general case) or is derived from the
predetermined path so as to take account of particular
circumstances. A typical example of a case in which the guidance
path is not the predetermined path which the vehicle should follow
is the final aircraft landing phase, after the descent phase, in
which the predetermined path is the axis of the runway since the
aircraft must complete the landing by taxiing along the runway, but
in which the guidance path is not the runway itself but is
preferably one parallel to the axis of the runway, situated below
the runway.
The main advantages of the invention are the following.
Firstly, it is easier to keep the movement symbol stable in the
guidance window when the vehicle is on the theoretical path which
it should follow or when it is immediately proximate to this
path.
On the other hand, it is now possible to make the aircraft follow a
continuous path guided by a discontinuous guidance path composed of
segments. For example, contrary to the prior art systems, an
aircraft can follow a predetermined path which comprises an ideal
line of descent, a flareout curve on approaching the point of
impact, and a taxiing line on the runway, this by using as guidance
path a simple succession of two straight-line segments which are
the ideal line of descent and a line parallel to the runway. The
flareout curve is then followed automatically by the aircraft by
the very principle of the invention, that is to say by the
principle of the pursuit of a fictitious point which is situated a
distance d ahead of the aircraft and which follows two successive
straight-line segments. In the prior art, the theoretical guidance
had to be interrupted ahead of the landing flareout.
The invention also makes it possible to follow a taxiing path on
runways segment by segment from landing up to the point of parking,
with a segmented guidance path and flareouts handled automatically
by the system.
Finally, an essential advantage of the invention lies in the
perception which the pilot has of the significance of the guidance
window which he sees on his screen. For sure, in the prior art, the
position of the window represented a datum direction to be followed
by the aircraft, but this direction did not correspond to any real
point in space towards which there would be reason to direct the
aircraft. The direction referenced by a fraction of the Glide
deviation altitude-wise and by a fraction of the LOC deviation
laterally does not in fact correspond to any physical point in
space having a particular significance for the pilot. And
additionally, the Glide and LOC deviations in the ILS system are
not even measured with respect to one and the same reference point
since the LOC deviation is referred to a point L at the end of the
runway whereas the Glide deviation is referred to a point G at the
start of the runway.
In the invention, the window, or more exactly its centre, indicates
to the pilot the direction of a point in space which is a datum
point actually situated on the guidance path. The pilot can
therefore mentally visualize this path, by imagining that the
window is situated on this path. In particular, during the descent
towards the runway, the pilot sees the runway on his screen in
realistic perspective and he is well aware that the ideal descent
path is a straight line directed towards the start of the runway
and along the axis of the runway. He can therefore easily imagine
the vertical descent plane and the window shows him, in an entirely
realistic manner, a point of this path situated the distance d
ahead of the aircraft.
This feature of the invention is very important since any pilot
navigating with the aid of instruments must have a very realistic
intuitive awareness of what his instruments are indicating to him
so that he can, if need be, immediately and intuitively compare the
indications from the instruments and the reality which he perceives
moreover directly.
Generally, the invention allows guidance of a vehicle on any
predetermined path by knowing this path and the position of the
vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood with the aid of the
descriptions based on the following figures:
FIG. 1, already described, depicts a view of the vertical plane
passing through the axis of a runway equipped with an ILS or
equivalent system.
FIG. 2, likewise already described, depicts a view from above of
the same runway.
FIG. 3 depicts datum points on a guidance path.
FIG. 4 depicts the aircraft and a segment of a specified path, seen
from above.
FIG. 5 depicts the vertical plane containing a segment of a
predetermined path.
FIG. 6 depicts a segment for linking up with a predetermined path,
the whole forming a guidance path.
FIG. 7 depicts the real path of a vehicle following the datum
according to the invention over a broken-line guidance path.
FIG. 8 depicts a display for assisting piloting.
FIG. 9 depicts a landing guidance datum of the ILS type (vertical
plane).
FIG. 10 depicts the same guidance datum (horizontal plane).
FIG. 11 depicts deviations in the vertical plane with respect to
the ideal line of descent.
FIG. 12 depicts a guidance window calculated according to the
invention.
FIG. 13 represents in perspective a landing guidance datum with two
segments, one of which is the axis of the runway.
FIG. 14 represents a guidance datum with two segments, the second
being situated under the axis of the runway.
FIG. 15 represents the general appearance of the display screen on
the approach to landing.
FIG. 16 represents the general structure of the navigation
assistance device using a head-up collimator computer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described in more detail with regard to the
piloting of an aircraft. It is assumed that the aircraft has,
conventionally:
means necessary for determining its own position at any
instant,
means for computing it track and its slope, that is to say the two
components of its real movement, which enable it to display a real
movement symbol (or velocity vector) on a display screen;
and that it also has data for a predetermined path or datum path
which it should follow or which it should join up with.
To make the explanation easier, it will firstly be assumed that the
guidance path which will serve in aiding piloting is exactly the
predetermined path which the aircraft should follow or join up
with. This predetermined path is defined in an exact form with
flareout curves between straight-line segments, or preferably in a
simplified form with straight-line segments only.
The computer on board the aircraft can therefore compute at any
moment that point F of the guidance path which is situated a
distance d ahead of the position P of the aircraft.
A guidance symbol will be displayed on the screen at a position
whose co-ordinates on the screen represent the two components
(vertical and
horizontal) of the direction connecting the point P to the point F.
FIG. 3 illustrates this principle of distance d between the
aircraft and a point of the datum path.
In FIG. 3, the guidance path T and the position P of the vehicle
are known in the same reference frame, for example a reference
frame fixed with respect to the earth. For the vehicle at the
position P, the guidance datum according to the invention is the
direction of the straight line connecting P to a datum point F such
that F belongs to the guidance path T, such that the distance PF
has the predetermined datum value d, and such that the point F is
ahead of the aircraft.
Thus F is the point of interception of the guidance path T and of
the sphere S with centre P and radius d. Naturally, only the point
of intersection situated ahead of the path will be retained.
The pilot, by modifying his direction of movement so as to approach
closer to the datum direction, will move his vehicle and when it
gets for example to the position P' represented in FIG. 3, the new
datum according to the invention, will be the straight line P'F',
where F' is on the path T and the distance P'F' has the value
d.
By considering, for example, the guidance path T formed of the
segment of predetermined path S.sub.i, the successive datum
settings supplied by the invention allow the vehicle to join up
with the predetermined path S.sub.i.
By way of example illustrated by FIGS. 4 and 5, the computation of
the datum point F is developed for a position P of the aircraft
with known latitude, longitude and altitude co-ordinates and for a
predetermined path formed of an oriented segment S.sub.i defined
with respect to the earth by the magnetic track .chi..sub.i, its
slope .gamma..sub.i and the co-ordinates of its culmination point
A.sub.i in terms of latitude, longitude and altitude.
The magnetic track is the angle .chi..sub.i, represented in FIG. 4,
between magnetic north and the oriented segment S.sub.i and the
slope is the angle .gamma..sub.i between the horizontal and the
vertical in the vertical plane containing the segment S.sub.i, and
represented in FIG. 5.
By considering the earth to be locally flat, a simple terrestrial
reference frame R.sub.N having the said point of culmination
A.sub.i as origin is the one corresponding to the three orthogonal
directions defined by magnetic North u.sub.N, East u.sub.E and the
vertical directed groundwards k. The said reference frame R.sub.N
(A.sub.i, u.sub.N, u.sub.E, k) is represented in FIG. 4.
Of course, the use of magnetic North is not obligatory, and
geographical North could equally well be used.
The device can consider the reference frame R.sub.i obtained by
rotation, of the above reference frame R.sub.N, by the angle
.chi..sub.i about the axis k. By considering the directions i and j
in the horizontal plane such that
and
the reference frame R.sub.i, with the point A.sub.i as origin and
with directions i and j supplemented with the vertical direction k,
allows a straightforward computation of the co-ordinates of the
datum point F for guidance.
Thus, the device, knowing the position P of the vehicle with
respect to the earth, can compute the abscissa x.sub.p, the
ordinate y.sub.p and the height z.sub.p of this position P in the
reference frame R.sub.i, i.e. P(x.sub.p, y.sub.p, z.sub.p).
Moreover, the guidance path corresponding to the predetermined path
formed by the segment S.sub.i is the straight line .DELTA..sub.i
supporting the segment S.sub.i. And in this same reference frame
R.sub.i, the straight line .DELTA..sub.i supporting the segment
S.sub.i satisfies the simple equation ##EQU1## whereas the sphere
SP with centre P and radius d satisfies the equation
The point F which makes it possible to define the datum in the
direction PF lies at the intersection of the sphere SP and of the
guidance line .DELTA..sub.i, its co-ordinates F(x, y, z) in the
reference frame R.sub.i satisfy the system of equations for the
straight line .DELTA..sub.i and also the equation of the sphere SP.
##EQU2## which can be expressed in the following form: ##EQU3##
The value of the abscissa x of the datum point F emerges from the
solutions of equation E3.
If two solutions exist, the device takes for example the larger
value.
Moreover, if the value retained is positive, the segment S.sub.i
has been passed, and it is then necessary to search for the
intersection with the next segment S.sub.i+1, of predetermined path
commencing at the culmination point A.sub.i of the segment S.sub.i
and finishing at the culmination point A.sub.i+1 of the next
segment S.sub.i+1.
If there is no solution, as in FIG. 6 where the consecutive
segments S.sub.i and S.sub.i+1 have no intersection with the sphere
S with centre P and radius d, the vehicle will be able to follow an
intermediate link-up segment S.sub.r so as to join up with the
segment S.sub.i. Such an intermediate segment is represented in
FIG. 6, it can be proposed by default as guidance by the device but
it can be defined by the pilot himself.
The vehicle at P is then directed towards the predetermined segment
S.sub.i by following the guidance according to the link-up segment
S.sub.r, and then when the vehicle is sufficiently close to the
segment S.sub.i, the datum is based directly on the segment
S.sub.i.
Thus, the device determines the point F which is the solution to
(E3) in the reference frame R.sub.i and, possessing the
co-ordinates of P in the same reference frame, it can compute
therein the co-ordinates of PF and finally express them in the
reference frame R.sub.N by applying the transformation
corresponding to the rotation -.chi..sub.i linking these two
reference frames.
By knowing the position P of the vehicle and the segment of
predetermined path S.sub.i it is possible for the device according
to the invention to compute the position of the point F on which
the datum direction is based and by knowing a segment S.sub.i+1
which follows S.sub.i it is possible to extend the datum relating
to the segment S.sub.i by that relating to the segment S.sub.i+1,
the datum point F sliding over the segment S.sub.i and then over
the next segment S.sub.i+1.
This guidance on a straight line, leads a vehicle which complies
with the datum to meeting the datum line tangentially, and the
stringing together of guidance segments leads the vehicle over a
real path joining the segments by tangent flareouts represented
dashed in FIG. 7.
The flareout is handled directly by this principle of guidance by a
point situated at a distance d and in accordance with broken
segments. This is what makes it possible to use, as predetermined
path to be followed by the aircraft, a simplified representation of
this path, in the form of successive segments, but it will be
understood that the invention is also applicable if the
predetermined path supplied to the computer is already an exact
path with predetermined flareouts.
Adjusting the distance datum d makes it possible to handle
flareouts of greater or lesser tightness. For example, it is
possible to fix a predetermined distance d1 for the altitude-wise
navigation paths, a distance d2 smaller than d1 to handle the
approach to and following of the descent path, and finally an even
smaller distance d3 to handle the landing proper, in particular to
handle the final flareout before the point of impact with the
ground.
The preferred embodiment of the device according to the invention
comprises a display device, fixed rigidly to the vehicle and whose
image projected in front of the pilot's eyes is represented in a
simplified form in FIG. 8.
In this image, a horizontal reference plane of the vehicle passing
through its centre of gravity is represented by a horizontal axis
53, a vertical reference plane of the vehicle passing through its
centre of gravity is represented by a vertical axis 54, and these
two axes 53 and 54 have an intersection at the point O. The
reference planes are those which correspond to a zero angle of
pitch and a zero angle of roll for the aircraft. An aircraft symbol
can be represented at the point O.
The moving horizon line 50 is defined with respect to the fixed
axes of the aircraft 53 and 54 by its position relative to the
point O and by its lateral tilt .phi. from the horizontal axis 53;
the tilt of the horizon line corresponds to the lateral tilt (roll)
of the aircraft, that is to say that due to the roll, the pilot who
is tied to the tilt of the aircraft sees the artificial horizon
line 50 tilt (exactly like the real horizon on which it is
superimposed). The distance OO' from the horizon line 50 to the
point O is proportional to the longitudinal tilt .theta. of the
aircraft (longitudinal attitude of the aircraft). The point O in
fact represents the projection at infinity of the longitudinal axis
of the aircraft above the horizon line. The lateral tilt .phi. and
longitudinal tilt .theta. are preferably supplied by an inertial
module mounted on the vehicle. The horizon line 50 can be
represented on the image by a continuous trace, it is graduated in
angular units of heading and the value of the heading of the
vehicle being supplied preferably by the said inertial module, the
graduation can be portrayed on the image by traces perpendicular to
this line and one degree distant for example. The graduation is a
360.degree. scrolling graduation.
The straight line passing through the point O and orthogonal to the
moving horizon line 50 is the longitudinal tilt line 51; it cuts
the moving horizon line 50 at the point O' representing the heading
of the vehicle, it is graduated in angular units so that the
distance OO' is a measure of the longitudinal attitude .theta.. A
heading symbol is displayed at the point O', the projection of the
point O onto the horizon line 50.
The velocity vector symbol displays the direction of real movement
of the vehicle with respect to the ground and is centred on a point
A. Its abscissa on the moving horizon line 50 represents the track
of the vehicle, a distance away from the point O' equal to the
value of the drift 6 which is the angle between the track and the
heading of the vehicle; the track is defined by the horizontal
component of the ground speed of the vehicle. The ordinate of the
point A on the longitudinal tilt line 51 represents the slope
.gamma..sub.S of the vehicle with respect to the ground, that is to
say an angle of descent with respect to the ground; the tangent of
the slope is equal to the ratio of the vertical component to the
horizontal component of the ground speed of the vehicle.
The velocity vector symbol is for example a circle 55 with centre A
supplemented with two dashes 56 and 57 situated on either side of
the centre A of the symbol on a straight line passing through the
centre of this symbol and parallel to the horizontal axis of the
vehicle 53.
In the image, the guidance symbol is centred on the representation
of the datum point F in real space. According to the description
above, the co-ordinates of the vector PF are known in the
terrestrial frame of reference R.sub.N, they therefore allow the
positioning, on the image in the vehicle at the position P, of the
representation of the datum point F. The co-ordinates of the centre
of the guidance symbol are referenced like those of the movement
symbol, with respect to the axes 50 (horizon line) and 51
(perpendicular to the horizon line through the point O). Thus, just
as the screen position of the real movement symbol represents a
direction of real movement of the aircraft expressed in terms of
track and slope, the position of the guidance symbol in the same
reference frame represents a datum direction to be followed by the
aircraft in terms of track and slope with respect to the axis of
the aircraft. And this direction is, according to the invention,
that of the vector PF, in which P is the position of the aircraft
and F is a distance d from the aircraft on the guidance path. The
co-ordinates of this vector PF are plotted on the screen as
components of track (along the axis 50) and of slope (along the
axis 51).
The purpose of assisted piloting is then to manoeuvre the aircraft
in a sense which tends to make the movement symbol join up with the
guidance symbol and remains centred on the latter. Specifically, if
the guidance symbol is to the left of the movement symbol (the case
of FIG. 8) according to the axis 50, the pilot must make the
aircraft turn to the left. If the guidance symbol is above the
movement symbol according to the axis 51, the pilot must reduce the
descent slope.
The guidance symbol is for example a rectangular window 58 centred
on the point F and whose dimensions reflect the acceptable
deviations with respect to the exact datum F. These deviations are
not necessarily the same in drift and in slope. And they are not
necessarily the same during all the phases of flight, landing and
taxiing.
The application of the invention will now be described in the case
in which the ideal path data are supplied by an ILS system to
define on the one hand the ideal line of descent towards a
theoretical point of impact G, and on the other hand the axis of
the runway on which the aircraft will taxi after impact. The
predetermined path to be followed is represented by an ideal line
of descent segment followed by a horizontal line segment on the
axis of the runway. The flareout will be handled automatically.
In the vertical plane represented in FIG. 9, passing through the
axis of the runway 11, the ideal line of descent 10, corresponding
to the guidance axis of the ILS beam, exhibits a tilt .theta..sub.0
with respect to the axis 11 of the runway, and an intersection with
the axis 11 of the runway at the point G.
An aircraft position cue is supplied by measuring, on the ILS
receiver aboard the aircraft, the angle EG between the two planes
passing through the horizontal axis comprising the point G and
orthogonal to the axis of the runway 11 and such that one of the
two planes contains the ideal line of descent 10 and the other
plane contains the point P representing the position of the
aircraft.
The altitude H of the aircraft is supplied for example by a radio
altimeter mounted on the aircraft. When the aircraft is close to
the ideal line of descent 10, itself of small tilt .theta..sub.0
with respect to the horizontal plane, the horizontal distance x
between the aircraft and the point P and the point G is simply
equal to the ratio of the altitude H of the aircraft to the tilt
.theta..sub.0 of the ideal line of descent plus the measure
E.sub.G. ##EQU4##
In the preferred embodiment of the device according to the
invention, a location cue for the a position P of the vehicle is
supplied by an ILS system, but a satellite locating system such as
GPS could also supply such a cue.
Once the aircraft is relatively near the guidance axis portrayed by
the ILS beam, the geometrical characteristics of the position of
the aircraft P, of the datum point F according to the invention,
and of the ILS system allow a simplified expression for the
position of the guidance symbol on the display means of the
piloting assistance device.
According to the invention, the datum point F belongs to the ideal
line of descent 10 and is the predetermined datum distance d away
from the position P of the aircraft.
Under the above assumption of the proximity of the aircraft to the
guidance axis, the altitude H.sub.F of the datum point F is
represented by the product of the tilt .theta..sub.0 of the ideal
line of descent 10 times the difference between the said horizontal
distance x and the predetermined datum distance d.
In the vertical plane of FIG. 9, the datum point F is seen by the
aircraft at an inclination .alpha. whose value is supplied to the
piloting aid symbol generator so as to define, for the image of
FIG. 8 projected in front of the pilot's eyes, the ordinate of the
centre of the guidance symbol along the longitudinal tilt line 51
referenced at the point O'.
The tilt .alpha. is the ratio of the difference in altitude between
the position of the aircraft P and the datum point F over the datum
distance d. ##EQU5## According to the invention, the ordinate
.alpha. of the centre of the guidance symbol is a function of the
following parameters supplied to the piloting assistance
device:
the inclination .theta..sub.0 of the ideal line of descent arising
from the information about the landing strips,
the altitude H of the aircraft as measured by the on-board radio
altimeter,
the measurement E.sub.G of the on-board ILS receiver
the predetermined datum distance d ##EQU6##
The predetermined datum distance d can be supplied by the pilot,
for example, by digital input or by selecting a value from a list
with the aid of a suitable device.
It can also be determined automatically by the assistance device
according to the invention from for example information about the
landing strip and about the design of the aircraft.
Measurement of the angle E.sub.G is no longer possible by the
receiver aboard the aircraft when the latter is very close to the
runway, that is to say a horizontal distance from the point G which
is less than the minimum distance x.sub.0 required for the validity
of the measurement of the angle E.sub.G.
After the aircraft has gone past the minimum distance x.sub.0, the
said horizontal distance x is no longer estimated by relation E4
but with the aid of an estimate of the distance travelled by the
aircraft as a function of its ground speed V supplied by the
inertial module mounted on board and of the time elapsed since it
passed the position corresponding to the minimum distance
x.sub.0.
Thus, in the absence of a measurement of the angle E.sub.G, the
ordinate of the centre of the guidance symbol is determined by the
symbol generator through the following relation ##EQU7##
FIG. 10 represents a view from above of the runway; the axis of the
runway 11 passes through the points G and L.
An aircraft position cue is supplied by measuring, on the ILS
receiver aboard the aircraft, the angle E.sub.L between the axis of
the runway 11 and the straight line 20 at the intersection of the
horizontal plane of the runway and of the vertical plane passing
through the point L of the runway and the position point P of the
aircraft.
The runway axis oriented from the entrance towards the exit of the
runway, hence from the point G towards the point L, exhibits a
heading of value T supplied by the information about the landing
strips together with the value d1 of the distance between the
points G and L.
The heading of the aircraft .psi. is supplied by the inertial
module mounted on board.
The angle .beta. is defined as the angle between the longitudinal
axis of the aircraft represented by its heading .psi. and the
straight line at the intersection of the horizontal plane of the
runway and of the vertical plane passing through the point G of the
runway and the position point P of the aircraft.
According to the invention, the value of the angle .beta. is
supplied to the piloting aid symbol generator so as to define, for
the image of FIG. 8 projected in front of the pilot's eyes, the
abscissa of the centre of the guidance symbol along the moving
horizon line 50 referenced at the point O'.
When the aircraft is close to the ILS guidance axis, the angle
.beta. is expressed with the aid of the horizontal distance x and
of the following parameters:
the heading of the runway T and the length of the runway d1 arising
from the information about the landing strips,
the heading of the aircraft .psi. supplied by the inertial module
mounted on the aircraft,
the measurement E.sub.L of the on-board ILS receiver,
the predetermined datum distance d according to the following
relation: ##EQU8## where the computation of the value of the
horizontal distance x was described above and summarized by
relations E4 and E8.
In the presence of turbulence, the centre of the guidance symbol
according to the invention has the advantage of remaining stable
with respect to the terrestrial environment seen by the pilot. This
makes it easier for the pilot to comply with the guidance
datum.
In the image projected in front of the pilot's eyes, the guidance
symbol is placed on the representation of the point F, it
preferably has the form, represented in FIG. 8, of a rectangular
window 58 with two sides parallel to the moving horizon line 50 and
two sides parallel to the longitudinal tilt line 51.
To follow the guidance datum according to the invention, the pilot
places the symbol for the velocity vector of his vehicle inside the
outline of the guidance window 58 and keeps it there, the
dimensions of this window reflecting the acceptable deviations
between the direction of the vehicle and the exact datum direction
represented by the point F.
In the vertical plane, the aircraft is regarded as deviating
excessively with respect to the ideal line of descent when it
leaves the beam determined by two descent planes.
This ideal descent plane is the plane passing through the ideal
line of descent with inclination .theta..sub.0 and through the
horizontal axis, represented by the line 22 in FIG. 10, comprising
the point G and orthogonal to the axis of the runway.
A beam, represented in FIG. 11, about the ideal descent plane is
defined by its lower plane 110 and its upper plane 111 which are
obtained by rotating the ideal plane about the horizontal axis 22
by the angles .epsilon. and .mu. respectively.
These angular values .epsilon. and .mu. can be proportional to that
of the inclination .theta..sub.0 of descent with proportionality
coefficients k.sub..epsilon. and k.sub..mu., for example equal to
0.12.
The datum window 58 is more precisely represented in FIG. 12. The
straight line 120 passing through its point F of centring on the
datum and parallel to the longitudinal tilt line 51 has two
intersections at the points Q and R with the sides of the
window.
The line 121 passing through its point F of centring on the datum
and parallel to the moving horizon line 50 has two intersections at
the points S and T with the sides of the window.
In the image projected in front of the pilot's eyes, the abscissae
of the points Q and R are equal to that of the centre of the
guidance symbol on the ideal line of descent with inclination
.theta..sub.0.
The ordinate .alpha..sub.R of the point Q can be equal to that of
the centre of a guidance symbol according to the invention
corresponding to a descent on the upper plane 111 defined by the
angles .theta..sub.0 and .mu..
And the ordinate .alpha..sub.R of the point R can be equal to that
of the centre of a guidance symbol corresponding to a descent on
the lower plane 100 defined by the angles .theta..sub.0 and
.epsilon..
In this case, .alpha..sub.Q and .alpha..sub.R are estimated through
the following relations ##EQU9##
However, the values chosen for the representation of the window
also comply with the constraints of presentation, the window having
to be visible without being too large in the image to allow the
pilot to follow the guidance.
In the horizontal plane, the aircraft must set its wheels down on
the runway, thus the limit of the guidance at the border of the
window at the point S can correspond to landing on an edge of the
runway, and that of the point T correspond to the other edge. Such
a width can be used throughout the guidance. However, a progressive
alteration in the width can also be used.
Moreover, the presentation of the window can vary depending on the
phases of the landing, in particular a modification of presentation
may be advantageous in order to remind the pilot of a change of
phase such as for example the start of a landing flareout where the
pilot will have to modify his altitude and slow down.
An enhancement of the invention to improve landing proper will now
be described, and it will be seen how in this case it may be
desirable for the computer to calculate a guidance path which
differs from the real predetermined path which the aircraft must
join up with and differs from the simplified representation of this
real path by segments.
Landing can be envisaged as the following of the particular datum
path, represented in FIG. 13, comprising a descent segment 90 and a
taxiing segment 91 on the axis of the runway 92.
The guidance according to the invention on such a path leads to a
soft landing tangential to the runway and represented by the dashed
curve 93, the accuracy of which would be insufficient for a landing
without the complementary aid of flight by sight. The accuracy of
the real point of impact is in fact sufficient only if the real
path of the aircraft intersects the runway at a non-zero angle. In
practice, in poor visibility a path angle of around one degree is
considered to be desirable at the moment of impact.
This is why it is proposed, in an enhancement of the invention,
that the guidance path be composed of a descent segment followed by
a segment parallel to the axis of the runway and situated under the
runway. This enhancement improves the accuracy of landing.
FIG. 14 represents a view of the vertical plane in line with the
axis 100 of the runway. The guidance according to this enhancement
of the invention on the consecutive segments, descent segment 101
and segment under the runway 102, with automatic handling of
flareout, leads to a real path, represented in this figure by the
dashed curve 103, whose real point of impact I with the ground is
more accurate than that obtained with a guidance segment coinciding
with the axis of the runway.
When the vehicle is already on the line of descent 101, the
automatic start-of-flareout due to such guidance is effected at the
distant d from the point 104 of change of guidance segment and
examination of the geometry represented in FIG. 14 makes it
possible to establish the two parameters of depth .DELTA.H of the
guidance segment 102 under the runway and of predetermined datum
distance d of such guidance.
This start-of-flareout is effected at the position P.sub.a of the
guided vehicle, whose altitude is equal to the value Ha and whose
guidance datum corresponding to this position P.sub.a is the point
A such that the distance between A and P.sub.a is equal to d.
The point P.sub.a and the point A being on the line of descent 101
with slope .theta..sub.0, their altitude deviation is related to
their distance through the following relation E24
After the start-of-flareout, the guidance datum follows the
horizontal segment 102 under the runway axis and when the vehicle
is at the real point of impact I, its guidance datum is the point B
of this segment 102 such that the distance IB is equal to d, and
the touch-down angle, defined as the angle .gamma. between the real
path and the ground, is the angle between the segment IB and the
segment 102 under the axis of the runway.
Thus, the depth .DELTA.H of this segment and the datum distance d
are related to the touch-down angle .gamma. by the following
relation E25:
If the touch-down angle .gamma. is different from the descent slope
.theta..sub.0, the pair of relations E24 and E25 is equivalent to
the following pair of relations E26 and E27: ##EQU10## which
determines the parameters of the guidance according to the
invention as a function of the imposed conditions of landing,
namely the descent slope .theta..sub.0 of around 3 degrees, the
touch-down angle .gamma. of around 1 degree and the
start-of-flareout height Ha imposed by the design of the vehicle
and supplied by its constructor.
By way of example, for a value of descent slope .theta..sub.0 of
three degrees and a value of touch-down angle .gamma. of one
degree, the value of the depth .DELTA.H of the guidance segment
under the runway is according to the invention equal to half the
start-of-flareout value.
Thus, for a realistic value of start-of-flareout height for an
average aircraft equal to 40 feet, horizontal guidance is sunk 20
feet under the runway axis and the datum distance is around 360
meters.
This datum distance d is that which applies during the terminal
phase of landing; the distance during the descent phase may be
different, and the distance during the previous phases of flight at
altitude may again be different.
The alterations in the distance law will be able to be sufficiently
regular as not to impair the continuity of piloting through jumps
in the guidance datum distance (which would be manifested as a jump
in the guidance window on the screen).
The above-described guidance according to the invention makes it
possible to guide not only the approach manoeuvre but also the
start-of-flareout and the flareout itself until impact with the
ground on the runway and it can be extended to the phase of taxiing
on the runway with the aid of an appropriate guidance datum,
corresponding to the horizontal movement alone. In the taxiing
phase after the point of impact G, the guidance path can continue
to lie beneath the runway or return to the axis of the runway since
the aircraft is no longer making a manoeuvre in three
dimensions.
During taxiing, the datum direction is horizontal, along the
segment PF, where the point F is on the axis of the runway at a
predetermined distance d adapted to the constraints of the
manoeuvres of the vehicle in this taxiing phase.
Given that the datum directions represented by the guidance symbol
must have a sense with respect to the pilot's eye (for compliance
with reality), whereas the pilot's eye is not in the plane of the
wheels of the aircraft, it will be possible to slightly correct the
position of the symbol displayed, in the final phases of landing
and in the taxiing phases, so as to give the pilot the most
realistic possible impression (the real movement symbol of the
aircraft is referred to the longitudinal axis of the aircraft which
is not situated at the height of the landing gear). The correction
made, for example at the moment of impact, will be able to be an
all-in correction taking account of the geometry of the aircraft
and of its attitude at the moment of landing.
Everything just stated with regard to assistance with piloting is
obviously applicable in a simulator since it is sought in a
simulator to reproduce exactly the real conditions seen by the
pilot. The only difference is that the vehicle position data are
supplied by computation by the simulator which does not move
instead of being supplied by instruments on board a vehicle which
does move.
To complete this description, FIG. 15 illustrates a representation
supplied to the pilot in the approach to a runway. The runway is
represented in perspective below the horizon line, the device
according to the invention displays a guidance window centred at
the point F which here is a point of the ideal descent path, so
that the pilot can easily make a concrete mental connection between
this window and the ideal line which he must join up with, that is
to say on the screen the straight line which connects the centre of
the window and the start G of the runway.
Naturally, the invention will be implemented with the aid of a
computer. This computer is preferably, as shown by FIG. 16, the
computer CALC which controls a head-up collimator HUD and which
receives to this end measurements originating from various sensors
CPT carried on board the aircraft, and especially sensors which
supply measurements of position, trim and speed.
* * * * *